This application claims the priority of Application No. 2001-272214, filed Sep. 7, 2001, in Japan, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an internal combustion engine diagnosis apparatus for diagnosing a catalyst to clean up a gas exhausted from an internal combustion engine, and particularly to an internal combustion engine diagnosis apparatus for diagnosing an HC adsorption catalyst which adsorbs HC when the internal combustion engine is in low temperature, and desorbs and cleans up HC when the internal combustion engine is in high temperature.
The exhaust gas (HC, NOx, CO) exhausted from an internal combustion engine can be cleaned up by a cleanup catalyst (ternary catalyst) arranged in an exhaust pipe. However, there has been a problem in that at starting of the internal combustion engine, HC is exhausted from the internal combustion engine until the cleanup catalyst is activated. Accordingly, a problem of reducing an amount of the exhausted HC still remains.
Therefore, a method of reducing exhaust of HC is proposed (refer to, for example, Japanese Patent Application Laid-Open No. 6-101452). The method employs an HC adsorption catalyst having a function of adsorbing HC exhausted from an internal combustion engine when temperature of the catalyst is low, and desorbing and cleaning up HC as temperature of the catalyst is increased.
FIG. 1 is a schematic diagram showing the cleanup principle of the HC adsorption catalyst. In the HC adsorption catalyst for cleaning up the HC at starting of the internal combustion engine, HC is adsorbed to zeolite during low temperature, as shown in FIG. 1 (a), and HC desorbed from the zeolite is oxidized on a noble metal, as shown in FIG. 1 (b).
Since degradation of adsorption performance of the HC adsorption catalyst is directly connected to degradation of the exhaust gas, utilizing the relationship between an adsorption amount of HC and an adsorption amount of water, U.S. Pat. No. 2,894,135 proposes an exhaust gas cleanup system for internal combustion engine. In the exhaust gas cleanup system, an adsorbent having a function of adsorbing HC in an exhaust gas under a given low temperature condition and an exhaust gas cleanup catalyst having a function of cleaning up pollution substances under a given high temperature condition are arranged in the exhaust system of the internal combustion engine. Under the low temperature condition before activating the exhaust gas cleanup catalyst, HC is adsorbed to the adsorbent. Under the high temperature condition after activating the exhaust gas cleanup catalyst, the HC adsorbed to the adsorbent is desorbed, and the desorbed HC is cleaned up by the exhaust gas cleanup catalyst. The proposed exhaust gas cleanup system for internal combustion engine comprises an operating state detection means for detecting an operating state of the engine; an exhaust gas temperature detection means for detecting exhaust gas temperatures at the inlet side and the outlet side of the adsorbent; an actual supplied heat equivalent value calculation means for calculating a value equivalent to an actual amount of heat supplied to the adsorbent from the exhaust gas based on the exhaust gas temperature and the exhaust gas flow rate in the inlet side of the adsorbent during dew-point period of the exhaust gas detected based on the state of the exhaust gas temperature in the outlet side of the adsorbent; an HC adsorption total amount estimation means for estimating an total amount of HC adsorbed to the adsorbent under a given adsorption condition based on the operating state of the engine; a reference supplied heat equivalent value calculation means for calculating a value equivalent to an amount of reference supplied heat supplied to the adsorbent in non-degraded state from the exhaust gas during the dew-point period of the exhaust gas based on the estimated total amount of adsorbed HC; and a degradation degree detection means for detecting a degradation degree of the adsorbent based on the calculated reference supplied heat equivalent value and the calculated actual supplied heat equivalent value.
Further, Japanese Patent Application Laid-Open No. 11-324659 proposes a system for diagnosing a degradation state of a hydrocarbon converting efficiency of a catalyst converter including a catalyst by measuring the catalyst temperature during the activation period. The system is a hydrocarbon converting efficiency degradation diagnosis apparatus for a catalyst converter which comprises a temperature sensor for continuously generating a first output signal expressing the catalyst temperature integrated with the catalyst converter; and a controller generating a second output signal for instructing the hydrocarbon efficiency of the catalyst converter based on variation of the catalyst temperature during the activation period.
However, the conventional diagnosing technology has the following problems to be explained below. FIG. 2 is a schematic graph showing the relationship between adsorption rate/cleanup rate and temperature of an HC adsorption catalyst. Degradation 1 shown in FIG. 2 indicates degradation of adsorption performance caused by thermal destruction of zeolite, and degradation 2 indicates degradation of activation performance (light-off performance) caused by thermal coagulation of the noble metal. Further, the HC adsorbed to the zeolite is desorbed in the catalyst temperature range of 50° C. to 250° C. though it depends on the operating condition of the internal combustion engine.
FIG. 3 shows the relationship between the amount of adsorbed HC and the amount of released or emitted HC without being cleaned up during being desorbed (the released HC amount). It can be understood from the figure that in the invention of U.S. Pat. No. 2,894,135, the degradation in the case of degradation 1 can be judged because the amount of adsorption is reduced, but the degradation in the case of degradation 2 can not be judged because the amount of adsorption is not reduced. Therefore, there is possibility that the degradation of exhaust gas can not accurately detect.
On the other hand, the technology described in Japanese Patent Application Laid-Open No. 11-324659 detects only the degradation of the light-off performance corresponding to the degradation 2 based on the variation of the catalyst temperature during operating period, and the heat of adsorption specific to the HC adsorption catalyst and the variation of heat capacity of the catalyst are not taken into consideration. Therefore, there is also possibility that the degradation of exhaust gas can not accurately detect.